Embodiments disclosed herein relate to the field of wavelength switched optical networks, or “WSON's”. More particularly, embodiments disclosed herein relate to methods and apparatus for reducing interruptions in data flow which may occur when a network element, node or connection fails or underperforms, by switching the data path through the network to a preselected alternate path that is maintained in a ready to receive mode.
WSON's employ fiber connected at optical cross connects, or nodes, at the data plane to carry a light based signal through a network. The optical signals are commonly multiplexed, i.e., more than one optical signal may be routed through an optical cross connection, but the different signals are transmitted at different wavelengths, so as to mitigate cross talk between the signals. Each optical cross connect is connectable to two or more light carrying fibers, such that light entering an optical cross connect may be selectively routed therefrom to one or more onward transmitting or carrying fibers. The selection of the light path, and configuration of the optical cross connects, is defined at the control plane of the network, which commonly includes a network control device for each optical cross connect in the data plane being controlled. The optical cross connect components may include one or more node elements, such as variable optical attenuators, or “VOA's”, regenerator devices which receive and transmit the optical signal after undertaking a noise reduction or other corrective action on the signal, or combinations thereof. Generalized multi protocol label switching protocol, or “GMPLS”, is commonly used for the control plane, although other protocols are used.
During operation of a WSON, one or more of the fiber or node devices may experience deterioration or failure, such that the resulting light signal passing therethrough is unacceptably degraded or lost. In such cases, the control plane of the WSON systems may then locate additional fiber pathways and node devices which are not in use, and switch the data stream which was passing through the now degraded or failed component(s) to these newly selected resources. This allows the WSON to recover and continue transmitting a data stream therethrough, but an unacceptable delay occurs during the recovery process caused in significant part by the need to turn on and tune the additional node devices to accept the signal. These components, which include variable optical attenuators (VOA's) and regenerators, must be brought on line, tuned to the frequencies of the wavelengths of the multiplexed light of the signal stream, and the amplification/attenuation of the signal adjusted to a desired level. For example, multiple channels (e.g., data transmitted on a respective carrier wave) may be multiplexed onto a single optical fiber. The nodes may include respective VOAs for each of the channels. The VOAs may attenuate the light associated with the channels such that the power of each channel is substantially the same. As such, when the optical signal is amplified before being multiplexed and transmitted to the next node, the amplitude of the light in each channel is the same, thereby mitigating cross talk between the channels. At the control plane, the detection of an optical impairment, and validation of a new or bypass routing, can take a few seconds. However, at the data plane, these steps can take as long as 2 to 3 seconds per node to adjust the power or attenuation/amplifications, and, where a node is being used that was not previously in use and was in standby mode, up to 10's of seconds to bring the node on line. Thus, where several nodes must be sequentially identified, activated, adjusted and tuned, the time to overcome a service interruption or unacceptable signal degradation may be in the range of minutes, which may result in poor network performance following the service interruption.